The present invention relates to a vehicle transmission including a torque converter and hydraulically operable transmission shift elements.
Powershift transmissions commonly utilize operating fluid at a regulated pressure, generally in the range of 180-200 psi, for effecting engagement of various transmission friction elements such as disc brake and clutch mechanisms. The source of this operating fluid is commonly a fixed-displacement pump operating against a pressure regulating valve for ensuring adequate pressure for operating the transmission shift elements. The pump, then, operates against regulated system pressure and, since the pump also normally supplies fluid for cooling and lubricating the transmission, it is of relatively large displacement. Thus, the power to drive the pump and the resultant heat load is significant.